1. Field of the Invention
The present invention relates to a disk recording and/or reproducing apparatus and a disk recording and/or reproducing method for recording (writing) and/or reproducing (reading) an information signal by rotating an optical disk and moving an optical pickup device along the information recording surface of the optical disk. More particularly, the invention relates to a tilt mechanism and method for adjusting the tilt angle of an optical pickup device with respect to an optical disk.
2. Description of Related Art
Hitherto, a disk recording and/or reproducing apparatus for recording and/or reproducing an information signal to/from an optical disk or magneto-optical disk, is generally known. In such a device, an optical disk is typically placed horizontally on a turntable. The turntable is attached to the rotary shaft of a spindle motor and is rotated. Simultaneously, the information recording surface of the optical disk is vertically irradiated with a laser beam emitted from an optical head of an optical pickup device. By moving the optical head from the center of the optical disk to the outer side in the radial direction, an information signal is written onto the information recording surface or the information signal recorded on the information recording surface in advance is read.
In such a disk recording and/or reproducing apparatus, the information recording surface of the optical disk and the optical head of the optical pickup device have to be mounted within a predetermined tilt range. This is because the reproduction accuracy of the information signal largely depends on the tilt of the optical head. In this case, in order to perform high-density and high-accuracy recording and/or reproduction of the optical disk, it is desirable to set the optical axis of the objective lens of the optical head perpendicular to the information recording surface of the optical disk. However, since the tilt of the optical disk, perpendicularity of the spindle motor, and perpendicularity of the objective lens vary, it is difficult to set the optical axis of the objective lens precisely perpendicular to the information recording surface of the optical disk.
In a disk recording and/or reproducing apparatus using an optical disk such as a CD, or a CD-ROM or the like, an allowable range of a relative tilt angle between the optical disk and the objective lens is standardized to less than or equal to 1.2° (the standard tilt angle of the optical disk is less than or equal to 0.6° and the standard tilt angle of the spindle motor or the objective lens is less than or equal to 0.6°). By tilting the optical pickup device from the state where the optical disk is mounted at a predetermined position as a reference, the optical axis of the objective lens is adjusted to be within a predetermined tilt range.
A disk recording and/or reproducing apparatus having a known tilt operating mechanism is shown in FIG. 23. A disk recording and/or reproducing apparatus 1 has a spindle chassis 2, a pickup chassis 3, and a tilt operating mechanism. The spindle chassis 2 is a plate-shaped frame body having a somewhat rectangular shaped opening. The pickup chassis 3 is a plate-shaped frame body which is slightly smaller than the spindle chassis 2 and similarly has an opening. The tilt operating mechanism rotates the pickup chassis 3 with respect to the spindle chassis 2 on the basis of the torque of a motor. The pickup chassis 3 has a pair of shafts 3a protruded from both sides in the width direction, while the spindle chassis 2 is provided with a pair of bearings 2a rotatably supporting the shafts 3a. By the combination of the pair of bearings 2a and the pair of shafts 3a, the pickup chassis 3 is supported by the spindle chassis 2 so as to be rotatable in the longitudinal direction.
The tilt operating mechanism 4 is provided on one side in the longitudinal direction of the spindle chassis 2. The pickup chassis 3 is rotatably operated in the longitudinal direction of the spindle chassis 2 by the operation of the tilt operating mechanism 4. On the other side in the longitudinal direction of the spindle chassis 2, a spindle motor 5 is fixed with its rotary shaft facing upward. A turntable 6, on which an optical disk is placed, is integrally attached to the rotary shaft of the spindle motor 5.
A guide shaft 3b and a guiding part (not shown) are attached so as to extend in the longitudinal direction in parallel to the pickup chassis 3 at a predetermined interval. The guide shaft 3b and the guide part slidably support a sliding member 8 of an optical pickup device 7. A rack (not shown) is fixed to the sliding member 8 and a gear, positioned at an end of a head feeding mechanism 9, engages with the rack. The head feeding mechanism 9 is driven and the rotary motion is transmitted to the sliding member 8, thereby moving the optical pickup device 7 toward or away from the turntable 6.
A tilt sensor 10, for sensing the distance from the information recording surface, is mounted on the sliding member 8. The tilt sensor 10 emits light toward the information recording surface and receives the light reflected by the information recording surface, thereby sensing a warp of the optical disk. The tilt operating mechanism 4 controls the tilt of the pickup chassis 3, on the basis of the sensing result of the tilt sensor 10, so as to minimize an error signal generated due to the warp of the optical disk. The tilt of the pickup chassis 3 is thereby changed and a tilt of the optical axis of the optical head 7a of the optical pickup device 7 with respect to the tilt of the information recording surface of the optical disk can be adjusted. Thus, when a disk recording and/or reproducing apparatus uses the tilt sensor 10, it is unnecessary to know a neutral point (mechanism center position) of the tilt operation.
A conventional disk recording and/or reproducing apparatus that includes a tilt sensor 10 to detect the optical disk warp has a high cost because of the tilt sensor 10. Moreover, the tilt control of the optical pickup device 8 is complicated, and the disk driving apparatus 1 is accordingly large. Further, since the tilt operating mechanism 4 has a tilt operation angle of about ±1°, there is also a problem that the mounting accuracy of the tilt sensor 10 has to be controlled rigorously.